(Inside Science) -- Most people assume they want control over how and when they work. But sometimes, too much autonomy can backfire, according to two new studies.

“The most surprising thing is that not everyone appears to want autonomy. It may be the case that autonomy is not desired by all people in all situations, and we need to take this into account before we seek to intervene,” said Bradley Wright, a psychology lecturer at La Trobe University in Victoria, Australia.

Wright is one of the authors of the first study, which found that participants performed worse and showed higher biological markers of stress when they had the power to choose when to take a break.

Researchers have known for decades that jobs with high demands and low autonomy seem to drain workers’ mental and physical health. For example, women with these types of jobs were 40 percent more likely to suffer from heart disease in a 10-year study of more than 17,000 women. Because of this pattern, it seems logical that employers can help workers with demanding jobs by giving them more autonomy.

In the new study, sixty female university students had two chances to alphabetize a reference list under time pressure. During one trial, the participants had to take a break at a set time, whereas in the other trial, they got to choose when to take their break.

Wright's team expected participants to find the interruption of the scheduled break frustrating, making them less productive and more stressed. Instead, they found the opposite. Rather than relieving pressure, the choice apparently exerted an additional cognitive burden, according to the authors. They aren’t sure why choosing a break time was so burdensome, but they think it may be related to the novelty of the situation. When people are starting a new job or learning a new skill, they might prefer “a little bit of hand-holding,” according to Wright. The study will be published January 2015 in the journal Psychoneuroendocrinology.

Jan Hausser, who studies workplace stress and health at the University of Hildesheim in Germany, agrees that more structure is helpful when people are first learning a job. However, he doesn’t think the novelty of the task explains Wright’s results, because the students who participated would have already been familiar with sorting reference lists.

Another study found that people vary in how much autonomy they want. Participants who focused more on preventing failure than on achieving success were happier, calmer and more productive when they had less control.

The study used a questionnaire to assess participants’ motivation. The questionnaire measured two types of focus. The first is called “prevention focus,” which is how much people focus on avoiding negative outcomes such as getting a failing grade. The other, “promotion focus,” describes the drive to excel and achieve goals. After completing the questionnaire, 110 university students played the role of a human resources manager answering emails from employees. For the first set of emails, participants had information about company policies but no specific instructions about how to do their jobs. Then, some participants were instructed to answer future emails in chronological order and at a consistent pace, while others were told they were free to choose their own order and pace.

The extra instructions had little effect on people with low prevention focus. However, those who focused on avoiding bad outcomes said they were more satisfied with the task when they had rules to follow and less satisfied when they were free to choose. The rules also increased productivity and reduced physiological stress in people who both feared failure and were not strongly motivated to excel. The results suggest that anxious or risk-averse people may do better in a structured environment where they know exactly what is expected of them, according to Stacey Parker, an organizational psychology lecturer at the University of Queensland in Australia and first author of the study. The study will be published this December in the International Journal of Psychophysiology.

“There’s a delicate dance that happens between every individual and their work situation. It’s really important to consider fit — how different peoples’ capabilities, needs, and preferences fit within their work structures,” said Parker. “If we can learn more about that, then hopefully we can optimize that fit so people are healthier at work and more productive.”

Nala Rogers is a science writer based in Santa Cruz, California. She tweets at @Nala_Rogers.